The invention relates to a device for measuring the density of a flowing medium such as a mixture of water and particulate material, in a pipeline, comprising a pipe section in loop form having two arms which make an angle with the horizontal, which arms each contain two pressure sensors which are located some distance apart in the direction of flow, as well as a processing unit, connected to the pressure sensors, for determining the density of the medium on the basis of the pressures or an associated parameter measured by the sensors.
A device of this type is disclosed in WO-A 95/04869. With this known device, the pipeline has a pipe section in loop form connected in series, which has approximately the same capacity (cross-sectional area) as the remainder of the pipeline. With this device the full flow of medium is fed through the pipe section in loop form.
In order to obtain a reliable measurement of the density, various conditions must be met. First of all the pressure sensors must be in a region of the arms of the pipe section in loop form where the flow is reasonably undisturbed. This means that they must be located in the straight section of the arms and, moreover, some distance away from the subsequent bend sections. This distance increases with the diameter of the pipeline.
Especially in the case of pipelines having a relatively large diameter, this leads to a section in loop form of appreciable dimensions, for example 5 to 12 meters high in the case of a vertical set-up of the arms. The cost of such a construction is appreciable.
The aim of the invention is to provide a device which does not have these disadvantages. Said aim is achieved in that the pipe section in loop form is connected in parallel to the pipeline.
Connecting the section in loop form in parallel offers the possibility of allowing the (main) pipeline itself to continue straight undisturbed. Only a faction of the flow of medium is diverted in order to perform a density measurement. As a consequence thereof, the cross-sectional dimension of the pipe section in loop form can remain restricted, which, in turn, has the consequence that the total height thereof can remain restricted. Nevertheless, a reliable density measurement can still be carried out in such a relatively small section in loop form since the flow has already become sufficiently quiescent a shorter distance away from the bend sections and has a relatively uniform character.
The connections from the pipe section in loop form to the pipeline can be some distance apart in the direction of flow of the medium through the pipeline. Incidentally, said connections can also be alongside one another.
To promote the measurement flow, the pipe section in loop form can contain a pump to promote the flow through the pipe section.